Punched holes in structural steelwork

Abstract

Abstract Punching is used as a cheap alternative to drilling in the fabrication of bolt-holes. When various steelwork standards are compared, it is seen that there is much variation in the restrictions imposed on punching. The history of brittle fractures associated with punching is reviewed. Background information is given on the way in which holes are punched, and on the metallurgical changes that are produced by punching. Evidence from previous research indicates that brittle behaviour only occurs when pronounced strain age embrittlement is caused by heating. A literature survey has revealed a few research programmes in which the effect of punching on the behaviour of bolted connections has been investigated. These programmes have been consistent in showing reductions in strength and ductility when punched specimens are compared to drilled ones. In view of the lack of relevant research on steels of recent British manufacture, a preliminary test programme on single bolt tensile splices was carried out. In contrast to the previous work mentioned above, this series of tests showed punched holes to have a greater bearing strength than drilled holes. One specimen failed in tension on the net section, and here there was a modest reduction in strength. With one exception, all specimens with punched holes had smaller ultimate deformations than those with drilled holes.